Because of the surrender bug, you shouldn't attack precursor ground forces; instead, let them attack you. But what if there are precursors on a planet who won't attack? Is bombardment the only option?
And when they have attacked me (at least I think they started it) and I finally win, my ships in orbit surrender, according to the log, but actually they just create empty task groups with the same name; they still belong to me. The planet is now "Vanquished/human" and my ground victorious troops are nowhere to be found.